The present invention relates to a method and apparatus for changing the moisture content of fibrous material, especially tobacco, and more particularly to a method and apparatus for changing the moisture content of fibrous material (hereinafter referred to as tobacco) by contacting tobacco with a gaseous fluid whose moisture content is normally different from that of tobacco. As a rule, the gaseous fluid is air which is conveyed in the form of one or more currents preferably flowing concurrent with the particles of a tobacco stream.
The treatment of tobacco leaves prior to conversion into fillers of cigarettes, cigarillos or cigars or into chewing tobacco involves a number of processes. The moisture content of tobacco leaves which are shipped by growers too processing plants is very low. Therefore, the resistance of such leaves to mechanical stresses is negligible, i.e., the leaves tend to break into smaller or larger fragments which is highly undesirable for a number of reasons. Consequently, the first stage of treatment of tobacco in a plant normally involves raising the moisture content well above the initial moisture content so as to insure that the next-following treatments, such as destalking of tobacco leaves, can be carried out without pronounced breakage. The moisture content of tobacco leaves prior to destalking, shredding and similar treatments must be maintained within a very narrow range, especially in modern tobacco processing plants where the treatment is fully automatic and the machinery for the processing of tobacco is supervised by a small number of semiskilled or even unskilled attendants.
German Auslegeschrift No. 1,145,530 discloses an apparatus for increasing the moisture content of tobacco wherein a stream of tobacco particles (e.g., leaves) is conveyed through a rotating drum and is contacted by a current of moist air which is caused to flow concurrent with the tobacco stream. There is no provision to regulate the temperature and/or moisture content of air so as to insure that the final moisture content of tobacco will not deviate from a predetermined optimum value or from a narrow range of optimum values.
U.S. Pat. No. 3,556,111 discloses a conditioning apparatus for Burley Tobacco. Such tobacco is heated to an elevated temperature in order to expel therefrom nitrogen gas which exerts an adverse influence on the taste and aroma of tobacco. The heating action is so pronounced that the moisture content of tobacco is automatically reduced to a very low value. Therefore, the tobacco must be caused to pass through a conditioning apparatus wherein its moisture content is raised by contact with currents of moist air which pass through a foraminous conveyor for a stream of tobacco particles. The air is moisturized by atomized liquid (normally water) and the rate of moisturization of air is regulated as a function of changes in the final moisture content of tobacco. Such regulation does not insure that the final moisture content of tobacco does not deviate appreciably from an optimum value. Moreover, the droplets of liquid which are carried by the currents of air are likely to be absorbed by tobacco particles which are first to come in contact therewith; this results in non-uniform wetting of tobacco.